In the related art, an image reading device used in digital copy machines and the like illuminates a document with linear light from a light source along a main-scanning direction, condenses reflective light from the document using lenses and the like, and allows the reflective light to be incident on an image sensor to read an image on the document.
As the light source for illuminating a document in the image reading device, for example, xenon lamps or light-emitting diode (LED) light sources are used. Methods for using LED light sources include a method of disposing a plurality of LEDs in a main-scanning direction to illuminate a document and a method of guiding LED light to a document surface using a light-guiding body to direct the light toward a document.
When a light-guiding body is used, LEDs are disposed at both ends of the light-guiding body, and light from the LEDs is scattered or reflected at the light-guiding body toward a document read area. Thus, the document read area is illuminated with the light. In addition, both ends of the light-guiding body are held in a holding unit by flat springs, and planar steps are disposed in both end portions of the light-guiding body to regulate movement of the light-guiding body in a main-scanning direction. The flat springs hold down the upper surface of the light-guiding body and are in contact with the planar steps of the light-guiding body on the side surface thereof to position the light-guiding body.
However, the planar steps in both end portions of the light-guiding body cause a radical change in the illuminance distribution in the vicinity of both ends of the light-guiding body, which results in substantial ripples in the illuminance distribution. When the illuminance distribution of the light-guiding body is not smooth, a shading process does not function correctly, and stripes occur in an image read from a document in a sub-scanning direction. Thus, reading performance may deteriorate.